Straightening or relaxing the curls of very curly hair is thought to increase the manageability and ease of styling of such hair. There is an increasing demand for the hair care products referred to as “hair relaxers,” which can relax or straighten naturally curly or kinky hair. Hair relaxers may either be applied in a hair salon by a professional or in the home by the individual consumer.
Hair fibre, a keratinous material, comprises proteins (polypeptides). Many of the polypeptides in hair fibres are bonded together or cross-linked with disulfide bonds (—S—S—). A disulfide bond may be formed from the reaction of two sulfhydryl groups (—SH), one on each of two cysteine residues, which results in the formation of a cystine residue. A cystine residue comprises a cross-link of the formula —CH2-S—S—CH2- between 2 polypeptides.
While there are other types of bonds which occur between the polypeptides in hair fibres, such as ionic (salt) bonds, the permanent curling or the shape of the hair is essentially dependent on the disulfide bonds of cystine residues.
As a result, relaxing or straightening of hair can be achieved by disrupting the disulfide bonds of the hair fibres with an alkaline agent or a −2 reducing agent. The chemical disruption of disulfide bonds by an alkaline agent is usually combined with mechanical straightening of the hair, such as combing, and straightening generally occurs due to changes of the relative positions of opposite polypeptide chains within the hair fibre. The reaction is generally terminated by rinsing and/or the application of a neutralizing composition. The reaction with the alkaline agent is normally initiated by hydroxide ions.
Specifically, hydroxide ions initiate a reaction in which a cystine cross-link (—CH2-S—S—CH2-) is broken and a lanthionine cross-link (—CH2-S—CH2-) is formed.
Consequently, the term “lanthionizing” is used when one skilled in the art refers to the relaxing or straightening of keratin fibres by hydroxide ions.
Hair that has been lanthionized using hydroxide ion generating compositions frequently feels harsh and can break during grooming.
Thus, there is still a need for compositions and methods to relax keratin fibres which preserve the relaxing efficiency of hydroxide ion yet do not cause the negative attributes associated with lanthionized hair.